absolute path is a path relative to the root directory, the topmost node of a hierarchical file system. Its first character must be a pathname separator, e.g., the Unix forward slash or MS-DOS backslash. absolute pathname is the full specification of a path beginning with the root directory /afs and including all directory levels the system passes through to locate the file.

access control list (acl) a list that specifies what access privileges users have to a directory, specifically, the right to lookup, insert, delete, read, write, lock, or administer files in a directory (abbreviated as l, i, d, r, w, k, a, respectively).

alias an alternate name or abbreviation (usually short and easy to remember) that substitutes for a pathname, command, list, or expression (usually long and hard to remember).

Andrew File System (afs) A distributed file system created in the Carnegie Mellon University Andrew Project, and later, a software product of Transarc Corporation, IBM, and OpenAFS. AFS distributes, stores, and joins files on networked computers. This distributed file system software makes it possible for users to access information located on any computer in a network.

argument information the shell needs to perform a command, usually the file(s) or entity that will be affected by a command. In a command statement, the argument follows the command, e.g., delete file, where delete is the command and file is the argument.

ASCII American Standard Code for Information Interchange a standard computer code used to facilitate the exchange of information on various types of data-processing equipment. Files are produced in or converted to ASCII code to make them easier to move into or out of software applications running on different machines.

Athena Project the joint project of MIT, DEC, and IBM in the 1980s that developed a distributed academic network for the MIT campus.

authentication the recognition of a user as having a valid account on the system with legitimate access to its resources, usually determined during login by username and password.

background process (bg) a program that runs without interfering with command entry and processing taking place in other windows. The & character added after a command will run that process in the background.

binary a number system in which the base is two, each number being expressed in powers of two by using only two digits, 0 and 1. A binary file is a program file built for the computer architecture. A binary server is a server computer on which the files of the operating system reside.

byte a unit of measure (8 bits) specifying file size, quota, and disk space.

cached file a copy of a file that the cache manager stores on a workstation's local disk.

cache manager a program on a client machine that accesses files stored in AFS. When a user requests a file, the cache manager retrieves it from the appropriate file server and stores or "caches" a copy of it on the client workstation's local disk for the user to use.

cache memory is a mechanism interposed in the memory hierarchy between main memory and the CPU to improve effective memory transfer rates and raise processor speeds. The name refers to the fact that that the mechanism is essentially hidden and appears transparent to the user.

cell an independently administered site running AFS and consisting of a collection of file server and client machines defined as belonging to the cell. A machine can belong to only one cell at a time.

client a program or machine that performs for a user, requesting files and information from a server program or computer in order to complete its function.

client/server a model for distributed network computing that relies on server computers to supply software and services to client computers that request them.

cluster a group of client workstations, usually close together, that connect off the same subnet.

command line interface a terminal-type means for sending commands to the shell and entering data into the computer. The command line is indicated by a symbol, or prompt (e.g., >, %, $), showing the user where to enter commands. Unlike a graphical user interface, this interface requires that commands be typed in and written in a precise syntax in order for them to be interpreted correctly by the shell.

console window the terminal window in which error and processing messages are written.

C shell (csh) a Unix shell developed by the University of California at Berkeley.

cursor a small symbol, often flashing, that indicates the user's place on the screen. It is the point-of-insertion indicator showing where data will be entered.

daemon a Unix system task that runs as a background process (usually initiated at system boot time) to perform a particular system function. Common Unix daemons control spooled printer output, accept incoming telnet requests, activate time-of-day scheduled tasks, etc.

default an automatic setting, mode, or action. Usually, there are alternative ways to perform any action in a computer program, but the default action is what will occur automatically if no other alternative is selected.

detached process a process that continues to run in the background after the user has logged out. Generally, a detached process is started when a user does not expect the process to finish during a session.

dialog box a small window-like box that opens after an operation has been selected. In it, you select options and settings to tailor the operation before it proceeds.

directory a special kind of file that points to or contains others files and directories. Directories can be nested to any depth. Some software may refer to directories and subdirectories by other names, such as, folders, lockers, file drawer, etc.

distributed file system a file system that joins together the file systems of individual machines. Files are stored (distributed) on different machines in a computer network but are accessible from all machines.

domain name system (DNS) a general-purpose distributed, replicated, data query service chiefly used on Internet for translating hostnames into Internet addresses.

dotfile see hidden file.

editor a program that allows the user to enter, alter, format and store program and text files.

environment variables global values or settings that determine the default operation of all shells and are also passed on to application programs. Environment variables contain information about your working environment. These are set by system administrators but can be changed by the individual user (main commands, printenv and setenv).

Eos name of the development project and the distributed AFS-based computing network in the NCSU College of Engineering. The technology is based on the Athena Project technology.

Ethernet a network communications protocol developed and originally marketed by Xerox Corporation. This technology is designed to handle the communication procedures of separate devices, such as word processors, personal computers, file and print servers, etc. Ethernet uses a bus technology, that is, it connects all stations on the network through a single channel of coaxial cable called a bus.

executable a statement or procedural step in a programming language that calls for processing action by the computer, e.g., performing arithmetic, reading data from an external medium, making a decision, etc. An executable file is a file with its mode is set to executable, making it a file that performs a process rather than simply holding data.

expression a series of fundamental elements making up a command statement that a compiler can use to produce a value. Expressions have one or more operands and, usually, one or more operators.

FDDI Fiber Distributed Data Interface a standard for fiber-optics network technology that specifies a 100 Mbs (100 million bits per second) data rate.

file a collection of information stored and retrieved under a single name.

file server a computer used to store files and transfer requested files to client machines. Also, the AFS fs command stands for "file server."

file system a set of many files organized in a hierarchical tree of directories and subdirectories.

filter a command that reformats or removes unwanted data from its input and writes the rest as output.

ftp Internet file transfer protocol for transferring files from one computer to another.

foreground process (fg) a process that engages the terminal so that it cannot be used for anything else until the foreground process has finished running. The shell must wait for the process to finish before prompting for another command.

gateway a device linking two networks that use different protocols. It accepts all packets from each network addressed to the other, buffers them, converts them to the next format, and re-transmits them to the other network.

graphical user interface (GUI) (pronounced "gooey") picture-based software, such as OSF/Motif, that employs window frames, icons, and pointers to interface with files and directories rather than commands. This graphical "front end" is designed to be easier for the user than issuing commands to the shell at the command line. A program with a GUI runs under some windowing system, such as X Windows in the case of Motif.

Hesiod a name coined by Project Athena for the "name-server" services of the network, which keeps track of resources and translates a request for a logical destination to a physical location. Named after the Greek poet, Hesiod.

hidden file a file that does not appear in directory listing, unless the user invokes the -a option, i.e., ls -a. Names of hidden files begin with a period, e.g., .mylogin; also called a dotfile.

home directory (~) a directory in a file system owned by a single user and used by that person to store files that s/he creates or copies there. The home directory is the directory the user enters upon login. It is represented by the tilde (~) in commands.

hostname the unique name by which a computer is known on a network, used to identify it in electronic mail, Usenet news, or other forms of electronic information interchange.

HTML Hypertext Markup Language a hypertext document format. Built on top of SGML and embedded as "tags" in .html files used on the World WideWeb.

http Hypertext Transfer Protocol the client-server TCP/IP protocol used on the World Wide Web for the exchange of HTML documents. It conventionally uses port 80.

hypertext information written, organized, and presented in an electronic "document" that has words or pictures linked to other documents. Hypertext is a document with embedded links that when selected connect the user to related text, graphics, or sound file.

icon a symbol or small picture on the display screen representing a software application or operation. Typically, a user points to or selects the icon with a pointing device, such as a mouse, to manipulate the program or operation in specific ways.

init process a process that begins execution when the system starts up and is responsible for creating login processes that wait for input from terminals. The init process is owned by the superuser and is controlled by the console.

Internet a worldwide complex of computer networks, communicating at high speeds using the TCP/IP protocol, which universities, companies, and governments use to exchange information, electronic mail, etc.

job a process or group of processes executed with a command, e.g., a print job, which is the process of sending and printing a file.

Kerberos a name coined by Project Athena for the authentication and security services of the network. Kerberos provides workstations and services with encrypted "tickets" to be used when requesting a service on the network. Named after Kerberos in Greek mythology, the three-headed dog that guards the gates of Hades.

kernel the central program and core of the operating system responsible for all machine-level work, including connecting to hardware devices. The kernel cannot be modified by the routine user.

LAN Local Area Network a data communications network which is geographically limited (typically to a 1 km radius) allowing easy interconnection of terminals, microprocessors and computers within adjacent buildings. Ethernet and FDDI are examples of standard LANs.

link a directory entry that refers to a file. There are two kinds of links-- hard and soft--both using the ln command. A hard link is indistinguishable from an original directory entry; it may not span file systems or refer to directories. A soft or symbolic link contains the name of the file to which it is linked; it may span file systems and refer to directories.

literal string a string of characters enclosed in quotation marks, which indicate that the string is to be interpreted literally.

locker a directory, often used to mean the collection of a main directory and all the subdirectories and files under it.

login or logging in the user-initiated process of gaining access to the system. Users identify themselves with their usernames and passwords, and the system verifies their accounts and permits them to access files and services.

logout or logging out the user-initiated process of signing off the system, including shutting down processes, putting away files, and cutting the user's connection to the system.

login id see username.

mail handler the user interface software for the mail system, which communicates with the Post Office server to access spooled user mail and deliver it to users on their display screens. This program also permits users to write mail message to other users.

man(ual) pages online reference documentation for Unix, organized by command into individual pieces or pages of explanation. For example, the command, man ls, brings up the man page on the ls command, which is further subdivided into parts covering the command's name, syntax, description, options, restrictions, etc.

MB1, MB2, MB3 abbreviations for the first, second, and third mouse buttons, respectively.

menu list of options and functions that users can "pull down" or "pop up" in places on the screen; user generally uses a mouse to select, and initialize operations from a menu.

metacharacter special characters that are neither letters nor numbers but have special meaning either to the shell or the operating system, e.g., > and <, which perform redirection, and |, which "pipes" commands. For a metacharacter to be interpreted literally and not for its special meaning, it must be placed in quotation marks, e.g., `<'.

mode bits a set of access rights associated with a file or directory in the Unix file system, which are shown with the ls -l command. The rights are read, write and execute (r,w,x). AFS combines their effect with AFS access rights in order to determine what type of access someone has to the files.

mount point a special type of directory that connects a location in the AFS file space with a volume. A mount point looks like a standard Unix directory. Listing the directory (ls) shows the contents of the volume.

mouse a hand-held locator and pointing device connected to the workstation by a cord.

multitasking able to support the processing of numerous programs and computations at the same time. Programs process concurrently and, thus, more quickly, permitting the easy sharing and movement of data, graphics, and text among windowed applications on the screen.

NFS a standard protocol developed by Sun Microsystems, which allows a computer to access files over a network as if they were on its local disks (similar to AFS).

node a connecting point on the backbone network. From nodes, bridges fan out to local ethernets.

operating system (OS) software (programs and data) that initiates the interaction of the electronic and electromechanical components of a computer so that they constitute a useful system for carrying out calculations; a set of instructions that tells a computer how to work. The operating system is the means for processing programs and sharing equipment and computer services among users.

operators symbols that represent processes to be carried out.

option an argument that controls how the shell executes a command, e.g., in the command ls -l, the -l is an option that tells the shell to do a special kind of directory listing, that is, a long listing of files.

partition an area of a computer disk used for storage and further subdivided into volumes.

password a unique, user-defined string of characters validating the user's system identity. The user must correctly enter the password (which does not appear on-screen when it is typed) in order to be authenticated by the system.

path is the specification of a file or directory in a hierarchical file system using pathname separators ("/" in Unix, "\" in MS-DOS) between directories. AKA pathname, the location of a file or directory in the system's hierarchical structure of directories. The pathname tells the shell where in the directory tree to find a file. Files may be referred to by absolute pathname (also called full or complete pathname) or relative pathname.

pid abbreviation for process abbreviation number (see process).

pipe ( | ) used to represent a pipe between two processes in a shell command line (see also pipeline).

pipeline a sequence of one or more shell commands separated by a pipe symbol ( | ). The standard output of each command is sent as standard input to the next command. Each command is run as a separate process, but the shell waits for the whole series to finish before issuing a new prompt.

PostScript a page description language that codes files for printing on PostScript printers.

process a job or program running on a computer. Unix assigns each process a unique reference number, called a process identification number (PID). Users refer to the PID when they want to affect a process in some way, such as to terminate it. A user identification number (UID) is also attached to every operating system process. When a user enters a Unix command, it is executed as a subordinate process, or child process of a parent process. Every process on the system has a parent except the init process (see init process). All processes that a user creates will be children of the login shell.

protocol a set of rules governing the communication and transfer of data between computers.

program a logical sequence of coded instructions specifying the operations to be performed by a computer in solving a problem or in processing data; or, a series of operations which may be used to control the function of an electronic device.

prompt a symbol, word, or message that the system displays to tell the user that it is ready for new input or commands. The default shell prompt of the Eos system is eos%.

quota a limit set by the system administrator on such things as disk storage (measured in kilobytes) and printing.

redirection the process of writing output from a command to a file using the right-angle bracket (>), or of reading input for a command from a file using the left-angle bracket (<).

relative pathname is the location of the file or directory relative to the directory in which the user is currently located (the current working directory).

remote access connection to the network from outside the established realm of client and server machines, usually via telephone and modem connection.

root directory ( / ) the top-level directory in the system's directory hierarchy, represented by the "forward slash" symbol ( / ).

router a dedicated computer that links, translates, and moves data in units called "packets" over networks.

scrolling the effect of lines moving on and off the screen or in and out of a window, either vertically or horizontally, as the user types or manipulates the cursor to move through a file that has been opened.

server a resource-sharing computer that shares its files and provides particular (usually specialized) support services to other computers on a network.

secure shell A Unix shell program for logging in and executing commands on a remote computer. ssh replaces rlogin and rsh and provides secure encrypted communications between two untrusted hosts over an insecure network.

shell a program that control user interactions with the kernel of the system by interpreting and executing commands. Sometimes called a command interpreter.

shell script a file of shell commands, also known as a shell program or shell procedure. Files having the # character as the first character are interpreted as C shell scripts.

shell variable a named storage location that contains a value. A value is assigned to a variable by using the set command. Shell variables work like environment variables, except that a set of shell variables is used by a single C shell only, and shell variables do not propagate to new shells or other programs.

standard input a file that represents where commands will get their input, which is usually from the keyboard. Typed commands are treated as standard input unless the user redirects the standard input to come from elsewhere.

standard output a file that represents where commands will send their output, which is usually to the terminal screen. When the system writes to the standard output file, the output appears on the screen unless the user redirects the standard output, such as to a file.

subdirectory a directory that resides in another directory.

superuser the administrator of the operating system. The superuser has special privileges, including the right to boot (start up) the system and to stop it, and to set up accounts and special user groups.

TCP/IP Transmission Control Protocol/Internet Protocol the formal rules (protocol) that the Internet uses to support such services as file transfer and mail.

telnet Internet standard protocol that runs on top of TCP/IP and acts as a terminal emulator for a remote login session.

terminal the combined keyboard and monitor through which the user communicates with the computer system.

ticket an encrypted protocol message that provides authentication; a type of access key conveyed in messages that allows the user to access services. If your tickets expires, you no longer have authenticated access and must log in again or kreset.

token a set of data that indicates that a user has been authenticated and is authorized to request files and services on the system. Tokens are granted after a user authenticates to AFS. A token is used by the Cache Manager when requesting services from AFS servers. A token has an associated lifetime and expires after a set period of time.

Unity the campus-wide implementation of the NCSU College of Engineering's computing environment, called Eos, a Unix-based network for distributed computing based on technology developed in MIT's Athena Project.

UNIX a popular operating system (of which there are many, e.g., GNU, Solaris, Linux, AIX, FreeBSD) that runs on many kinds of computers. It is a multi-user, time-sharing operating system more than 30 years old. It has been developed by many programmers in an open-source model of shared source code and cross-platform portability.

URL Uniform Resource Locator a simple extension of the standard filename concept. It can be used to point to files and directories on any machine connected to the network. It can be accessed through several different methods, e.g., ftp, gopher and HTTP.

username or userid a short string of characters (usually 8) entered at login that uniquely identifies a user. Also called the login id, the username is the first thing typed into the computer and, together with the password, is used to authenticate user accounts on the system.

variable a symbol whose value can be set.

vi a full-screen editor available to Unix users.

volume a container that keeps a set of related files and directories together on a disk partition (specific to AFS), e.g., a user's home directory.

wildcard a metacharacter that can be used in place of other characters or words in filename arguments. The asterisk (*) and question mark (?) are wildcards.

window manager A part of a window system which arranges windows on a screen. It is responsible for moving and resizing windows, and other such functions common to all applications.

word wrap allows you to type continuously without pressing RETURN to start a new line because the program "wraps" the text to the new line for you.

working directory the directory the user is currently working in. Typically, when users log in, they are placed in their home directories, which would be their working directory. The command pwd (path of working directory) tells what the user's working or current directory is.

World Wide Web international effort to organize the Internet's data and information resources into hypertext formats that are linked together and searchable.

X11 a network protocol and subroutine library used to create graphic images and windows.

X Window System A specification for device-independent windowing operations on bitmap display devices, developed initially by MIT's Project Athena and now a de facto standard supported by the X Consortium. X uses a client-server protocol, the X protocol. The server is the computer or X terminal with the screen, keyboard, mouse and server program and the clients are application programs. Clients may run on the same computer as the server or on a different computer, communicating over Ethernet via TCP/IP protocols. X clients often run on what people usually think of as their server (e.g., a file server) but in X, it is the screen and keyboard etc. which is being "served out" to the applications.

Zephyr a name coined by Project Athena for the rapid user-notification and message service on the system. Messages are sent from a terminal window with the zwrite command and received and displayed in a window on the receiver's screen. Named after Zephyr, god of the West Wind and son of Eos and Astraeus in Greek mythology.

Information Technology and Engineering Computer Services (ITECS)
College of Engineering, North Carolina State University, Raleigh, NC 27695
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